Asynchronous Transfer Mode (ATM) connection services and Frame Relay (FR) connections are typically implemented using Permanent Virtual Circuit (PVC) connections and Switched Virtual Circuit (SVC) connections. For example, an PVC connection via an ATM network, the virtual channel identifier (VCI) and virtual path identifier (VPI) values are manually configured at each switching point in the connection, typically at each interface of network devices such as switches, routers, and switch-routers. In an ATM cell header, for example, the VCI and VPI are a 16-bit field and a 8-bit field, respectively. In PVCs, the VCI and the VPI are used to identify the next destination of a cell as it passes through a series of ATM switches on its way to its destination. ATM switches use the VPI/VCI fields to identify the next network virtual channel link (VCL) that a cell needs to transit on its way to its final destination. In a FR network, a data-link connection identifier (DLCI) is used in place or the VPI/VCI identifier. A value of the DLCI specifies a PVC or an SVC in a similar manner as the VPI and VCI. The manual configuration of VPI/VCI or DLCI values, though tedious, is required only once, because the PVC connection remains up permanently once the connection is set up. Thus, PVC connections are typically used for connections that are always or frequently in use or high-demand connections.
SVC connections are suitable for connections that are infrequently in use or short-lived connections. Using signaling, SVC connections are dynamically established on demand and are released when the connection is not being used. That is, end systems (typically source-end systems) request connectivity to other end systems (typically destination-end systems) on an as-needed basis, and if certain criteria for the connection are met, the connection is set up at the time of request. When the connection is no longer needed, for example, the transmission is completed or terminated, it is dynamically torn down, freeing network bandwidth. The same SVC connection can be brought up again when it is requested. In addition, if one link in an SVC connection fails, the SVC connection is automatically rerouted around the failure through the communications network.
The third type of connections are a hybrid of the PVCs and SVCs, referred to as Soft Permanent Virtual Circuit (Soft PVC or SPVC) connections. FIG. 1 schematically illustrates a typical SPVC 10 which includes PVC connections 12 and 13, and an SVC connection 14. For example, as shown in FIG. 1, the PVC connection 12 is set up from an edge router 16 to a network device 18, the SVC connection 14 is set up from the network device 18 to another network device 20 via a communications network 22, and the PVC connection 13 is set up from the network switch 20 to a destination device (typically an edge router) 24. In a typical mode of configuration, the edge routers 16 and 24 are “un-trusted” edge routers outside a secured or private network, and the SVC connection 14 is set up inside a “trusted” network such as a Service Provider network or a private corporation network.
Although an SPVC connection is a permanent connection, it allows end devices (for example, the routers 16 and 24 in FIG. 1) attached to the network devices to be interconnected via an SVC connection, which will be automatically rerouted around failures in the link through the communications network as mentioned above. For example, as shown in FIG. 1, an SVC is dynamically created, using link A or link B. If either link fails, the SVC is automatically reestablished using the other link. In addition, since SPVC connections are set up through signaling (other than explicitly configured PVC connection(s) at end systems), the need for extensive manual configuration is substantially reduced.
FIG. 2 schematically illustrates a Soft PVC 30 connecting user A 32 and user D 34 through the ATM communications network 36. Unlike hard PVCs, the interface and VPI/VCI identifiers are configured only for the endpoints of the connection. For example, a PVC connection leg 38 is configured on a network device (switch B) 40 with an interface (0/0/0) and VPI/VCI values (0, 200), and another PVC connection leg 42 is configured on a network device (switch C) 42 with an interface (3/0/0) and VPI/VCI values (0. 100). The VPI/VCI values for the intermediate switching points, for example, an SVC connection leg 46 for the network device 40, an SVC connection leg 48 on the network device 44, and all other links though the ATM communications network 36, are not required to be configured, since these are dynamically determined by signaling.
There are two modes of SPVC configurations: single-ended SPVC connection provisioning and double-ended SPVC connection provisioning. In the single-ended SPVC connection provisioning, SPVCs are configured at the source endpoint (for example, the PVC connection leg 38 on the network device 40) and do not require configuration of a passive or destination endpoint (for example, the PVC connection leg 42 on the network device 44). Single-ended SPVCs are easier to configure and the passive endpoint is automatically created by the source endpoint. However, there is no guarantee that a single-ended SPVC can get the bandwidth or connection identifiers at the passive endpoint (destination network device) as requested from the source endpoint.
In the double-ended SPVC provisioning, users are required to configure a passive endpoint (for example, the PVC connection leg 42 on the network device 44) of a Soft PVC connection. However, this allows resources on the terminating switch (destination network device) to be reserved for the incoming SPVC connection, and usage parameter control (UPC) options can also be configured for individual SPVCs for traffic policing. Furthermore, packet discard options for congestion control may also be configured.
Double-ended SPVCs are advantageous over single-ended SPVCs in the following situations.
In the case where SPVC and SVC services are running on the same interface, the destination end VPI/VCI values are not “stolen” by an incoming SVC connection during a re-routing of an exiting SPVC connection. In the single-ended SPVC configuration, as soon as the SPVC is de-routed, the endpoint is deleted and the VPI/VCI values are released. Thus, the VPI/VCI values can be assigned to any incoming SVC call before reestablishing the SPVC connection and completing the re-routing. This is the same for an SPVC connection that is not in currently connected state and thus the VPI/VCI values can be assigned to an incoming SVC call. Furthermore, during an attempt to modify the traffic parameters of an exiting SPVC connection, the same problem may happen in single-ended SPVCs.
In addition, in single-ended SPVCs, when a source network device makes a request (call) to an SPVC address on a destination network device, the destination (passive) network device would simply accept the call, and any source network device can make such a call. Thus, two (or more) SPVCs with the same destination address and the same VPI/VCI values could be configured from different source network devices, and this is especially problematic in a multi-vendor environment. In double-ended SPVCs, however, the source end and destination end must “match,” i.e., the service category, Peak Cell Rate/Sustained Cell Rate (PCR/SCR), and other parameters must be configured the same on both ends, avoiding such conflicting connections.
However, matching the service category, PCR/SCR, and other parameters is not a perfect solution, since even in the double-ended SPVCs, there are cases where an SPVC connection from one endpoint is inadvertently mis-configured to reach a wrong destination, and the service category, PCR/SCR, and other parameters of the mis-configured connection can match, especially, when these parameters have default values. Such mis-routing traffic due to configuration errors may have significant consequences. Furthermore, in connection-oriented networks using ATM communications, bandwidth and specific connection identifiers may be reserved for premium subscribers, and such configuration errors and mis-routing may result in depriving the subscribers of their premium services by unauthorized use.
Accordingly it would be desirable to provide a method and apparatus for controlling double-ended SPVC connections that solve the above-mentioned problems.